My present invention relates to a machine tool and, more particularly, to a machining center having a multiplicity of stations at which machining operations can be carried out. Also the invention relates to a machining center of the type in which the multiplicity of machining stations are arrayed about a central axis.
A machining center having a central axis and a multiplicity of positions or stations at which machining can occur arrayed around the axis is known. The machining center can be used primarily for the machining of metal workpieces by turning, milling, drilling or the like machining operations. They enable, for example, one workpiece to be machined at a first station while other workpieces are machined at other stations and each workpiece to be transferred from a first to a second station and so on until the machining operations are completed. The machining center permits not only a succession of different machining operations to be carried out upon a given workpiece but also a number of workpieces to be operated upon simultaneously to thereby increase productivity, reduce machining time and minimize the machining cost. When, in addition, the workpiece transfer between stations or positioning of the workpiece at the respective station is effected automatically, manual intervention is reduced to a minimum, and cost is similarly reduced.
In German patent document DE 195 04 369 Al, a multispindle machine tool is described which has a multiplicity of spindles in a frame rotatable about an axis, the spindle each engaging a workpiece and being rotatable. The arrangement of the spindles in this system is, however, fixed relative to the frame and the entire frame can be set into rotation in increments of, for example 45xc2x0 about the central axis so that the workpiece on each spindle is presented to a new working station or sector at which it can be engaged by a tool.
The tools in each sector can then be moved towards the workpiece to allow machining of the latter when it is set into rotation through the respective spindle or even while it is at standstill.
The fixed arrangement of the individual spindle with respect to the axis, even with the freedom of rotation of the spindles between stations, has the disadvantage that the tool in each working sector or machining station must be movable toward and away from or relative to the workpiece. In point of fact the tools are mounted to enable radial movement of the tools relative to the spindles. The positioning of the workpieces on the spindles at the work stations is then exclusively by the rotation of the entire spindle assembly and each spindle may be vertically displaceable to vary the vertical position of the workpiece holder at each station.
The horizontal position of each workpiece in the particular machining sector or station is fixed and usually located along a center line through the particular sector or station. In German patent document DE 199 16 212 Al, the spindles within a sector or station can be movable along a predominantly circular path. This allows a spindle unit to cooperate within each machining sector or station with, for example, two different tools while in at least one other station the spindle is not moved. This permits various machining processes, some of which can be more time extensive than others, to be optimally combined with each other. It also enables a more flexible arrangement or use of the tools in the individual machining stations or sectors.
Nevertheless this machine has the disadvantage that within each sector only a limited number of tools can be arranged. Additionally for the system of DE 199 16 212 as well as that of DE 195 04 369, after a complete machining cycle, the array of spindles is periodically rotated back through about 360to return the individual spindles to their starting positions when extensive slide contacts and distributors are to be avoided for the electrical and fluid lines. A further drawback is that in each machining sector the tool must be mounted for radial shiftability when a relative radial movement of the workpiece and tools is required for the machining purpose. For each tool, therefore, there must be a corresponding feed and guide arrangement which has its own drive and that can be costly, especially when a large number of tools is provided.
It is, therefore, the principal object of the present invention to provide a machine tool and especially a machining center whereby the aforementioned drawbacks are avoided.
Another object of the invention is to provide, in a machine tool of the aforedescribed type, an arrangement which reduces the cost for multi-axis machines, limits the size of the machining stations which are required for that purpose and ensures reduction in time for multi-step machining operations.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention in a machine tool and especially a machining center having a spindle unit, also referred to as a work spindle unit which is mounted to orbit a central axis and, of course, can be rotatable about its own axis. At least one such spindle unit is provided so that it can be positioned in at least one but preferably a plurality of positions spaced around the central axis and so that at least some of the stations can be provided with tool units. The at least one work spindle unit, in addition, is movable in the radial direction relative to the central axis and, in an embodiment of the invention, across or through this axis to a position or station at the opposite sides of the orbit.
The movement of the at least one work spindle unit in the radial direction may be independent of any positioning movement thereof of the workpiece relative to the work spindle unit and independent of any positioning movement of the tool or tools at the particular station.
The system of the invention, therefore, provides that the workpiece, which can be mounted on the work spindle unit, can be shiftable in the radial direction within a machining sector or station independently of any positioning movement required for the machining practice at that station itself. The work spindle unit, by being orbital about the central axis can position the workpiece at any of the machining sectors or stations thereby contributing additional degrees of freedom of movement and especially the freedom of movement of the radial direction, or movement of the workpiece so as to place the workpiece in a position where it can be attacked by a tool at that station, i.e. for positioning the workpiece and/or for the machining itself or to allow selection of the tool which is to engage the workpiece.
Through this additional radial mobility of the work spindle unit it is possible to dispose tools along various partial circular paths or circular path segments in any of the machining sectors or stations for contact with the workpiece so that a feed device can be eliminated for all or for some of the tools at the particular sector or station or such that none of the tools or not all of the tools need be provided with respective feed units.
In combination with the vertical mobility of the workpiece, each can be provided by the working spindle unit, each machining sector or station can have a multiplicity of tools at different spacings from the central axis and at different vertical positions or heights for respective contact with the workpiece.
The radial movement of the work spindle unit can be decoupled advantageously from the positioning movement of the spindle unit. The term xe2x80x9cpositioning movementxe2x80x9d when referring to the spindle movement will be understood to be that movement of the workpiece which causes machining when the workpiece engages a tool. That will be understood to be distinct from the radial movement of the workpiece holder, namely, the work spindle unit which has been referred to before and may be provided in addition to the positioning movement and may, for example, enable the workpiece to be displaced linearly to position the axis to the opposite side of the orbit.
The work spindle unit is held in a frame or support which can receive a plurality of work spindle units, each of which is capable of the aforementioned radial displacement. If this frame is rotated, say 45xc2x0 about the central and usually vertical axis to position the work spindle unit and workpiece at successive machining sector or station, the orbit can encompass eight such stations and the frame can have two radially movable work spindle units disposed at diametrically opposite sectors or stations and each being radially displaceable to position its workpiece for engagement by any number of tools at the particular sector. A selected one of the work spindle units, of course, can be capable of radial displacement at any selected sector while another radial spindle unit is fixedly positioned on the frame at its sector if desired. This allows, for example, a machining process to be carried out for a relatively long time in the latter sector while in the former two or more different machining steps can be carried out which are shorter in time with the workpiece being positioned first at the one tool and then by radial displacement to a tool further from the central axis or closer to the central axis by a second tool.
Advantageously the frame is in the form of a bridge which can be rotated about the central axis and has been found to be an exceptionally stable structure for supporting one or more work spindle units. The bridge may be symmetrically designed to extend over all of the sectors or stations and to be guided on a track of path which surrounds the machining sectors or stations. The bridge or bridge unit, upon which the work spindle units are movable radially with respect to the central axis may have generally radial guide members upon which the work spindle units or carriages are shiftable. The path formed by the track is usually circular and the bridge may be supported thereon with line or surface contact via suitable sliding shoes and plane bearings or roller bearings or wheels to provide sufficient stability to the support of the bridge. The bridge can have two opposite legs which ride upon the track and can be supported thereon with suitable support surfaces. Of course, the bridge can have a cruciform shape and can be supported with four legs or feet on the track.
The bridge is driven, according to a feature of the invention by at least one drive in such manner that it is rotated point symmetrically about the central axis. For a uniform force transfer it is also conceivable to provide a plurality of drives distributed uniformly over the periphery of the orbit or located at opposite sides thereof. In such cases linear drives can be contemplated.
In an advantageous embodiment of the invention the path provided on the bridge for the work spindle unit can extend substantially over the entire length of the bridge. This is desirable for the case in which a single work spindle unit is intended to carry a workpiece from a station or sector on one side of the axis to a station and center on the opposite sides of the axis, possibly in a successive step. In this case, the spindle is moved substantially along a diameter of the circle defined by the track or constituting the orbit of the ends of the bridge. The transfer of a workpiece by the work spindle unit from a first machining sector to one on the opposite sides of the center can thus be accomplished in the shortest possible time or with a time saving.
The positioning of a work spindle unit which is displaceable along the track of the bridge can be effected advantageously in the following manner. The work spindle unit is initially brought to a first spindle region, i.e. a machining sector or station, on one side of the bridge unit and can be swung exclusively by rotation of the bridge itself through not more than 180xc2x0 about the central axis to one-half of the machining sectors and shifted to the other half by radial displacement over the length of the bridge to the sectors lying on the opposite side also through 180xc2x0. The machining can thus be effected in one sector after the other over the arc of 180on the one side and when the machining is required in any of the other sectors, i.e. outside the original 180xc2x0 arc and on the opposite side of the orbit, the work spindle unit is displaced radially on the track of the bridge to the sector on the other side. Once there, of course, it can be moved to any of the sectors along the other 180xc2x0. The system, therefore, allows the bridge to rotate back and forth through 180xc2x0 without having to make a full revolution while ensuring the possibility of machining the workpiece at any of the sectors. Within each machining sector or station, the spindle unit can, by displacement to a greater or lesser radial extent or by raising and lowering the spindle effect machining with a variety of tools at the particular station or sector as may be desired.
According to a feature of the invention a control unit can be provided which so regulates the swinging movement of the bridge and the movement of the working spindle unit from one to another end of the bridge or radially along the bridge as a function of the machining space to be carried out and to minimize the total machining time for a particular workpiece.
Of course the bridge may be rotated through more than 180xc2x0 although a rotation in excess of 360xc2x0 is not desirable so as to avoid for complicated slip rings or devices for distributing fluid to a rotating element.
The displacement of the work spindle unit along the bridge track can be rapid and can take place during angular displacement of the bridge, thereby permitting rapid transfer of a workpiece from one machining sector or station to another. The selection of the processing steps which can be carried out is simple so that the control unit not only has the advantage of optimizing the machining times but also step selection and combinations of machining steps to be practiced.
In a further advantageous embodiment of the invention a multiplicity of mutually and rigidly interconnected bridge units are provided. Each bridge unit can carry a working spindle unit which is displaceable in the aforedescribed manner, i.e. radially at least limitedly toward and away from the axis. The bridge can extend across the diameter of the orbital circle if desired and two further bridge units may be attached thereto and can be located parallel to one another and to the right and left of the centrally oriented bridge unit. Each of these bridge units may have a respective working spindle unit radially shiftable thereon so that each unit can be displaceable from one end to another of the particular bridge unit. The maximum displacement of a work spindle unit which is not mounted on a central bridge unit is thus shorter than the displaceability of the work spindle unit on the central bridge unit. In spite of this construction, even here and movement of the work spindle unit from one to another end of the bridge is possible and allows another machining sector or station to be selected which may not be directly opposite its original sector or station but rather may be a neighboring machining sector or station.
The result is the ability to provide a multiplicity of work spindle units and appropriate bridge structures which in combination with rotation of the bridge and radial displacement of the work spindle arrangement provides a highly flexible positioning of workpieces by a multiplicity of sectors and stations.
In another advantageous embodiment of the invention, a bridge unit is provided on which two work spindle units can be radially displaceable. In this case, each work spindle unit can be movable within a limited range and within its limited range can position the workpiece in engagement with a number of tools. The work spindle unit cannot be displaced here from one end of the bridge to the other but by doubling the number of work spindle units on a bridge can increase the number of work pieces being machined at a given time and thereby reduce machining time for a number of such workpieces.
The radial mobility of the two work spindle units can be achieved with the previously-mentioned track on the bridge and that track can extend the full length of the bridge although each unit may be displaceable over only a limited portion of that length.
The bridge unit can be so configured that it has a plurality of arms or allows three or more work spindle units to be spaced apart about the axis. Each spindle unit can be radially displaceable within a range and the bridge unit in that case will have the shape of a star whose arms are angularly equispaced at 120xc2x0 relative to one another, each arm carrying one of the work spindle units.
Similarly the bridge can have more than three arms and work spindle units and it is preferred to provide a number of arms which are angularly equispaced about the central axis and each of which carries a respective work spindle unit. The number of arms can equal the number of sectors or machining stations. In the case of a system having five work spindle units, the bridge may have the shape of a five-pointed star.
In a further embodiment of the invention at least one of the work spindle units is so mounted on the bridge that in addition to its radial displaceability it may have a freedom of movement also in a tangential direction, i.e. in a direction perpendicular to the vertical and radial directions. This means that the work spindle unit, after it has been positioned in a sector or station by the bridge can be moved not only in the radial direction but also transverse to that direction, i.e. generally toward one of the adjoining sectors or vertically or both. This provides an additional measure of flexibility and freedom for machining the workpiece with a multiplicity of tools per machining sector or station.
The bridge unit can have crossing tracks or paths for the working spindle unit and on each of these crossing tracks one or two work spindle units can be provided. The work spindle units thus can be displaceable at right angles to one another, preferably in the same plane and preferably across the central axis so that each work spindle unit is movable along its imaginary linear path on the bridge.
The swingable displacement of the bridge can be effected basically to position the work spindle unit at a machining station or segment for a certain machining operation. The swinging movement which can be a partial displacement of the bridge about the central axis can be in either direction or can be replaced by rotation through more than 360xc2x0 if desired. The swinging movement can in addition be in part a machining movement with the workpiece in contact with a tool so that during the movement of the bridge one or more workpieces may also be machined.
The radial movement of the work spindle units along the bridge can be completely independent of the pivotal movement of the bridge so that one can take place before or after the other or both can take place simultaneously. However, a mechanical coupling of the movements or a coupling using the control for the movement can be effected if desired. The movement of the workpiece thus need not be a linear or simple arcuate movement but can be a movement representing superimposition of the tangential and radial movements of the bridge and the work spindle unit. The composite movement allows a three-dimensional positioning of the workpiece while rotation of the spindle allows the latter to be rotated as well during a machining operation.
The positioning of the workpiece at the sectors or stations is intended primarily for machining the workpiece at each sector or station. However one or more sectors or stations may be used to mount the workpiece on the work spindle unit or remove the workpiece from it, the mounting and its mounting of the workpiece being effect manually or by suitable automatic mounting and dismounting means.